The present invention relates to a method for range and offset adjustment and calibration of nondispersive infrared gas analyzer provided for the determination of concentration of a gas component having a basic concentration that is relatively high while the variations in concentration that are of interest cover but a relatively small level and range.
Gas measuring engineering and technology is frequently faced with the task of measuring a gas component and constituent, as well as variations thereof which are basically very small as compared to a "background" of a relatively large basic concentration. This measuring problem at hand is complicated particularly when the basic concentration of the measuring component changes continuously or frequently, thereby obliterating the range and variance of interest. An example is the measurement of assimilation on the basis of the heretofore used optical methods. Here one uses the so called Lambert-Beer law which yields a nonlinear relation between the absorption of light radiation on the one hand, and concentration of a gas in the medium passed through by the light on the other hand. If the sensitivity changes in time depending on the basic concentration, one has to provide a continuous range tracking.
In the example mentioned above the assimilation of interest involves the CO2 content in air. This concentration, considered as a background, may depend on conditions that vary between about 320 ppm and 1000 ppm. Since the assimilation covers only small variations such as 50 ppm in the CO2 value measuring range, background variations can easily obliterate measurement errors up to 50% and more may readily arise.